Grafted syndiotactic polypropylene and coextruding binders based on syndiotactic polypropylene

ABSTRACT

A coextrusion binder and a multilayer structure containing the binding wherein the binder contains a composition comprising (I) syndiotactic polypropylene and (II) at least one polymer being:
         (A), a polyethylene or a copolymer of ethylene,   (B), any of (B1) isotactic polypropylene homopolymer of copolymer, (B2) poly(1-butene) homo- or copolymer or (B3) polystyrene homo- or copolymer,   and a blend of (A) and (B),
 
said composition being grafted with a functional monomer such that each of I and II is at least partially grafted with said functional monomer.

BACKGROUND OF THE INVENTION

The present invention relates to syndiotactic polypropylene where on hasbeen grafted a functional monomer. This product is of use as acompatibilizing agent, for example in blends of polyamide and ofpolypropylene or in blends of polypropylene and of glass fibres. Thesyndiotactic polypropylene is also of use as a coextrusion binder.

The coextrusion binder is composed (i) either of grafted syndiotacticpolypropylene then optionally diluted in at least one polyolefin (C1) orin at least one polymer with an elastomeric nature (D) or in a blend of(C1) and (D), (ii) or of grafted isotactic polypropylene diluted insyndiotactic polypropylene and optionally in at least one polymer withan elastomeric nature (D).

These coextrusion binders are of use, for example, in the manufacture ofmultilayer materials for packaging. Mention may be made of materialscomprising a film of polyamide (PA) and a film of polypropylene (PP), itbeing possible for the polypropylene film to be laminated onto thepolyamide film or coextruded with the polyamide. The coextrusion binderis positioned between the polypropylene and the polyamide for goodadhesion of the PA and of the PP. These multilayer materials can bethree-layer structures PP/binder/EVOH in which EVOH denotes a copolymerof ethylene and of vinyl alcohol or a partially or completelyethylene/saponified vinyl acetate (EVA) copolymer or five-layerstructures PP/binder/EVOH/binder/PP.

PRIOR ART AND TECHNICAL PROBLEM

Polypropylene is described in Kirk-Othmer, Encyclopaedia of ChemicalTechnology, 4th edition, Vol. 17, pages 784-819, John Wiley & Sons,1996. Virtually all polypropylene sold is composed essentially ofisotactic polypropylene possibly containing a small amount of atacticpolypropylene.

Numerous prior arts exist disclosing grafted polypropylene but it isalways isotactic polypropylene.

Patent U.S. Pat. No. 5,235,149 discloses packagings closed by capscomposed of an aluminium sheet, of a binder layer and of a polypropylenelayer. The binder layer of the cap is composed of various polymersgrafted with acrylic acid or maleic anhydride; the polymers can bechosen from polyethylene, polypropylene, copolymers of ethylene and ofvinyl acetate and copolymers of ethylene and of methyl acrylate.

Patent DE 19 535 915 A discloses a grafted polypropylene block copolymerfor adhesively bonding polypropylene films to metal sheets.

Patent EP 689 505 discloses structures similar to those disclosed in theabove patent but which are used to prepare food packagings.

Patent EP 658 139 discloses structures similar to those disclosed in thepreceding patent but the binder is a grafted random polypropylenecopolymer comprising from 1 to 10% of comonomer, the Mw/Mn ratio isbetween 2 and 10 and the MFI (Melt Flow Index) is comprised between 1and 20 g/10 min (230° C., 2.16 kg).

The radical grafting of functional monomers to polyolefins is carriedout either in the molten state, or in solution, using radicalinitiators, such as peroxides, or in the solid state, by irradiation.Under the action of the radicals, side reactions occur at the same timeas the grafting reaction. They result in an increase in the molecularmass in the case where the polymer to be grafted is polyethylene or inits decrease in the case where this is polypropylene. If the amount ofradicals necessary for the grafting reaction is high, the change in themolecular mass of the polyolefin results in a significant modificationin its melt viscosity. These grafting operations are generally carriedout in an extruder. The viscosity of the grafted polyethylene is so highthat it is no longer possible to extrude it; the viscosity of thegrafted polypropylene is so low that it too can no longer be extruded.These phenomena reduce the amount of reactive functional groups whichcan be incorporated into the polyolefin by radical grafting offunctional monomers.

Patent EP 802 207 discloses the grafting of large amounts of functionalmonomer to blends of polyethylene and of polypropylene. The increase inthe molecular mass of the polyethylene is compensated for by thedecrease in the molecular mass of the polypropylene present during theradical grafting reaction. Generally, this blend of cograftedpolyethylene and polypropylene is subsequently diluted in a polyolefin.

It has now been found that a functional monomer can be grafted tosyndiotactic polypropylene and that the melt flow index (also denoted byMFI) increases much less than if isotactic polypropylene were grafted.It is thus possible to graft amounts of functional monomer which canreach 4 to 8% by weight of the syndiotactic polypropylene. This solutionis simpler than to graft a blend of polypropylene and of polyethylene.

BRIEF DESCRIPTION OF THE INVENTION

The present invention relates to syndiotactic polypropylene to which hasbeen grafted a functional monomer.

The invention also relates to a coextrusion binder composed (i) eitherof grafted syndiotactic polypropylene then optionally diluted in atleast one polyolefin (C1) or in at least one polymer with an elastomericnature (D) or in a blend of (C1) and (D), (ii) or of grafted isotacticpolypropylene diluted in syndiotactic polypropylene and optionally in atleast one polymer with an elastomeric nature (D).

The present invention also relates to a multilayer structure composed ofa layer comprising the preceding binder and, directly attached to thislayer, a layer of nitrogen-comprising or oxygen-comprising polar resin,such as a layer (E) of a polyamide resin, of a saponified copolymer ofethylene and of vinyl acetate, of a polyester resin, of an inorganicoxide deposited on a polymer, such as PE, poly(ethylene terephthalate)or EVOH, or else a metal or metalloplastic layer.

According to another alternative form, the invention also relates to thepreceding structure with, directly attached to the latter, on the sideof the binder, a polyolefin-based layer (F).

DETAILED DESCRIPTION OF THE INVENTION

Syndiotactic polypropylene is described in Kirk-Othmer, Encyclopedia ofChemical Technology, 4^(th) edition, Vol. 17, pages 784-819, John Wiley& Sons, 1996. Advantageously, its MFI (in g/10 min at 190° C., 2.16 kg)is at most 10 and advantageously between 0.1 and 3.

Mention may also be made of the syndiotactic polypropylene disclosed inpatents U.S. Pat. Nos. 5,969,021, 5,710,222, 5,688,735, 5,476,914,5,334,677, 5,292,838, 5,278,265, 5,243,002, 5,225,500, 5,223,468,5,223,467, 5,155,080 and 4,892,851.

It would not be departing from the scope of the invention if thesyndiotactic polypropylene were to comprise at least one polymer chosenfrom (A), denoting a polyethylene or a copolymer of ethylene, and (B),itself chosen from (B1) isotactic polypropylene homopolymer orcopolymer, (B2) poly(1-butene) homo- or copolymer and (B3) polystyrenehomo- or copolymer. That is to say that a blend comprising eithersyndiotactic polypropylene and (A), or syndiotactic polypropylene and(B), or syndiotactic polypropylene and (A) and (B), is grafted.Advantageously, the proportion of (A) and/or (B) represents less than40% by weight of the combination of syndiotactic polypropylene and (A)and/or (B).

(A) is chosen from polyethylene homo- or copolymers.

Mention may be made, as comonomers, of the following:

-   -   α-olefins, advantageously those having from 3 to 30 carbon        atoms. Examples of α-olefins having 3 to 30 carbon atoms as        possible comonomers comprise propylene, 1-butene, 1-pentene,        3-methyl-1-butene, 1-hexene, 4-methyl-1-pentene,        3-methyl-1-pentene, 1-octene, 1-decene, 1-dodecene,        1-tetradecene, 1-hexadecene, 1-octadecene, 1-eicocene,        1-dococene, 1-tetracocene, 1-hexacocene, 1-octacocene and        1-triacontene. These α-olefins can be used alone or as a mixture        of two or of more than two.    -   esters of unsaturated carboxylic acids, such as, for example,        alkyl (meth)acrylates, it being possible for the alkyls to have        up to 24 carbon atoms.

Examples of alkyl acrylate or methacrylate are in particular methylmethacrylate, ethyl acrylate, n-butyl acrylate, isobutyl acrylate or2-ethylhexyl acrylate.

-   -   vinyl esters of saturated carboxylic acids, such as, for        example, vinyl acetate or propionate.    -   unsaturated epoxides.

Examples of unsaturated epoxides are in particular:

-   -   aliphatic glycidyl esters and ethers, such as allyl glycidyl        ether, vinyl glycidyl ether, glycidyl maleate, glycidyl        itaconate, glycidyl acrylate or glycidyl methacrylate, and    -   alicyclic glycidyl esters and ethers, such as        2-cyclohexene-1-glycidyl ether, diglycidyl        cyclohexene-4,5-carboxylate, glycidyl cyclohexene-4-carboxylate,        glycidyl 2-methyl-5-norbornene-2-carboxylate and diglycidyl        endo-cis-bicyclo[2.2.1]hept-5-ene-2,3-dicarboxylate.    -   unsaturated carboxylic acids, their salts and their anhydrides.

Examples of unsaturated dicarboxylic acid anhydrides are in particularmaleic anhydride, itaconic anhydride, citraconic anhydride andtetrahydrophthalic anhydride.

-   -   dienes, such as, for example, 1,4-hexadiene.    -   (A) can comprise several comonomers.

Advantageously, the polymer (A), which can be a blend of severalpolymers, comprises at least 50 mol % and preferably 75 mol % ofethylene. The density of (A) can be between 0.86 and 0.98 g/cm³. The MFI(viscosity index at 190° C., 2.16 kg) is advantageously comprisedbetween 1 and 1000 g/10 min.

Mention may be made, as example of polymers (A), of:

-   -   low density polyethylene (LDPE)    -   high density polyethylene (HDPE)    -   linear low density polyethylene (LLDPE)    -   very low density polyethylene (VLDPE)    -   polyethylene obtained by metallocene catalysis, that is to say        the polymers obtained by copolymerization of ethylene and of        α-olefin, such as propylene, butene, hexene or octene, in the        presence of a single-site catalyst generally composed of a        zirconium or titanium atom and of two cyclic alkyl molecules        bonded to the metal. More specifically, the metallocene        catalysts are usually composed of two cyclopentadiene rings        bonded to the metal. These catalysts are frequently used with        aluminoxanes as cocatalysts or activators, preferably        methylaluminoxane (MAO). Hafnium can also be used as metal to        which the cyclopentadiene is attached. Other metallocenes can        include transition metals from Groups IVA, VA and VIA. Metals        from the lanthamide series can also be used.    -   EPR (ethylene/propylene rubber) elastomers;    -   EPDM (ethylene/propylene/diene) elastomers;    -   blends of polyethylene with an EPR or an EPDM;    -   ethylene/alkyl (meth)acrylate copolymers which can comprise up        to 60% by weight of (meth)acrylate and preferably from 2 to 40%;    -   ethylene/alkyl (meth)acrylate/maleic anhydride copolymers        obtained by copolymerization of the three monomers, the        proportions of (meth)acrylate being as the above copolymers, the        amount of maleic anhydride being up to 10% and preferably 0.2 to        6% by weight;    -   ethylene/vinyl acetate/maleic anhydride copolymers obtained by        copolymerization of the three monomers, the proportions being        the same as in the above copolymer.

As regards (B1), this is an isotactic polypropylene homo- or copolymer.Mention may be made, as comonomers, of:

-   -   α-olefins, advantageously those having from 3 to 30 carbon        atoms. Examples of such α-olefins are the same as for (A),        except that propylene is replaced by ethylene in the list,    -   dienes.

(B1) can also be a copolymer comprising polypropylene blocks.

Mention may be made, as example of polymer (B1), of

-   -   polypropylene,    -   blends of polypropylene and of EPDM or of EPR.

Advantageously, the polymer (B1), which can be a blend of severalpolymers, comprises at least 50 mol % and preferably 75 mol % ofpropylene.

B2 is chosen from poly(1-butene) or the copolymers of 1-butene withethylene or another α-olefin having from 3 to 10 carbons, except thepropylene already mentioned in (B1).

(B3) is chosen from polystyrene or styrene copolymers. Mention may bemade, among the copolymers, by way of example, of dienes having from 4to 8 carbon atoms.

As regards the functional monomer, it is unsaturated, mention may bemade, by way of example, of alkoxysilanes, carboxylic acids and theirderivatives, acid chlorides, isocyanates, oxazolines, epoxides, aminesor hydroxides.

Mention may be made, among alkoxysilanes carrying an unsaturation, of:

-   -   CH₂═CH—Si(OR)₃ vinyltrialkoxysilanes    -   CH₂═CH—CH₂—Si(OR)₃ allyltrialkoxysilanes    -   CH₂═CR₁—CO—O—Y—Si(OR)₃ (meth)acryloxyalkyltrialkoxysilanes (or        (meth)acrylsilanes) in which:

R is an alkyl having from 1 to 5 carbon atoms or an alkoxyl —R₂OR₃ inwhich R₂ and R₃ are alkyls having at most 5 carbon atoms for thecombination of R₂ and R₃.

R₁ is a hydrogen or a methyl.

Y is an alkylene having from 1 to 5 carbon atoms.

Use is made, for example, of vinylsilanes, such astrimethoxyvinylsilane, triethoxyvinylsilane, tripropoxyvinylsilane,tributoxyvinylsilane, tripentoxyvinylsilane ortris(β-methoxyethoxy)vinylsilane, allylsilanes, such astrimethoxyallylsilane, triethoxyallylsilane, tripropoxyallylsilane,tributoxyallylsilane or tripentoxyallylsilane, or acrylsilanes, such asacryloxymethyltrimethoxysilane, methacryloxymethylmethoxysilane,acryloxyethyltrimethoxysilane, methacryloxymethylmethoxysilane,acryloxyethyltrimethoxysilane, methacryloxyethyltrimethoxysilane,acryloxypropyltrimethoxysilane, methacryloxypropyltrimethoxysilane,acryloxybutyltrimethoxysilane, methacryloxybutylmethoxysilane,acryloxyethyltriethoxysilane, methacryloxyethyltriethoxysilane,methacryloxyethyltripropoxysilane, acryloxypropyltributoxysilane ormethacryloxypropyltripentoxysilane.

Use may also be made of mixtures of these products.

Use is preferably made of:

-   -   CH₂═CH—Si—(OCH₃)₃ vinyltrimethoxysilane (VTMO)    -   CH₂═CH—Si—(OCH₂CH₃)₃ vinyltriethoxysilane (VTEO)    -   CH₂═CH—Si—(OCH₂OCH₂CH₃)₃ vinyltrimethoxyethoxysilane (VTMOEO)    -   and (3-(methacryloxy)propyl)trimethoxysilane        CH₂═C(CH₃)—CO—O—(CH₂)₃—Si (OCH₃)₃

Examples of unsaturated carboxylic acids are those having 2 to 20 carbonatoms, such as acrylic, methacrylic, maleic, fumaric and itaconic acids.The functional derivatives of these acids comprise, for example, theanhydrides, the ester derivatives, the amide derivatives, the imidederivatives and the metal salts (such as the alkali metal salts) of theunsaturated carboxylic acids.

Unsaturated dicarboxylic acids having 4 to 10 carbon atoms and theirfunctional derivatives, particularly their anhydrides, are particularlypreferred grafting monomers.

These grafting monomers comprise, for example, maleic, fumaric,itaconic, citraconic, allylsuccinic, cyclohex-4-ene-1,2-dicarboxylic,4-methylcyclohex-4-ene-1,2-dicarboxylic,bicyclo[2.2.1-hept-5-ene-2,3-dicarboxylic andx-methylbicyclo-[2.2.1-hept-5-ene-2,3-dicarboxylic acids and maleic,itaconic, citraconic, allylsuccinic, cyclohex-4-ene-1,2-dicarboxylic,4-methylenecyclohex-4-ene-1,2-dicarboxylic,bicyclo[2.2.1]hept-5-ene-2,3-dicarboxylic andx-methylbicyclo[2.2.1]hept-5-ene-2,2-dicarboxylic anhydrides.

Examples of other grafting monomer comprise C₁-C₈ alkyl esters orglycidyl ester derivatives of unsaturated carboxylic acids, such asmethyl acrylate, methyl methacrylate, ethyl acrylate, ethylmethacrylate, butyl acrylate, butyl methacrylate, glycidyl acrylate,glycidyl methacrylate, monoethyl maleate, diethyl maleate, monomethylfumarate, dimethyl fumarate, monomethyl itaconate and diethyl itaconate;the amide derivatives of unsaturated carboxylic acids, such asacrylamide, methacrylamide, maleic monoamide, maleic diamide, maleicN-monoethylamide, maleic N,N-diethylamide, maleic N-monobutylamide,maleic N,N-dibutylamide, fumaric monoamide, fumaric diamide, fumaricN-monoethylamide, fumaric N,N-diethylamide, fumaric N-monobutylamide andfumaric N,N-dibutylamide; the imide derivatives of unsaturatedcarboxylic acids, such as maleimide, N-butylmaleimide andN-phenyl-maleimide; and metal salts of unsaturated carboxylic acids,such as sodium acrylate, sodium methacrylate, potassium acrylate andpotassium methacrylate.

Various known processes can be used to graft a grafting monomer onto thesyndiotactic polypropylene optionally comprising (A) and/or (B).

For example, this can be carried out by heating it at high temperature,approximately 150° C. to approximately 300° C., in the presence orabsence of a solvent, with or without a radical initiator. Appropriatesolvents which can be used in this reaction are benzene, toluene,xylene, chlorobenzene, cumene and the like. Appropriate radicalinitiators which can be used comprise t-butyl hydroperoxide, cumenehydroperoxide, diisopropylbenzene hydroperoxide, di(t-butyl) peroxide,t-butyl cumyl peroxide, dicumyl peroxide,1,3-bis(t-butylperoxyisopropyl)benzene, acetyl peroxide, benzoylperoxide, isobutyryl peroxide, bis(3,5,5-trimethylhexanoyl) peroxide andmethyl ethyl ketone peroxide.

The syndiotactic polypropylene and optionally (A) and/or (B) can be dryor melt preblended and can then be grafted in the molten state or insolution in a solvent. They can also be added separately to a device forbringing into contact and blending (for example, an extruder), togetherwith the grafting monomer and the radical initiator. Use may be made ofthe usual mixing and blending devices of the thermoplastics industry.

The amount of grafting monomer can be appropriately chosen but it ispreferably from 0.01 to 10%, better still from 0.1 to 5%, with respectto the weight of the grafted polypropylene, optionally comprising (A)and/or (B). The amount of grafted monomer is determined byquantitatively determining the succinic functional groups by FTIRspectroscopy.

The invention also relates to a coextrusion binder composed:

either (1), according to a first form, of grafted syndiotacticpolypropylene then optionally diluted in at least one polyolefin (C1) orin at least one polymer with an elastomeric nature (D) or in a blend of(C1) and (D),

or (ii), according to a second form, of grafted isotactic polypropylenediluted in syndiotactic polypropylene and optionally in at least onepolymer with an elastomeric nature (D).

As regards the first form, the binder is therefore composed of thegrafted syndiotactic polypropylene which was described above and whichis optionally diluted in at least one polyolefin (C1) or in at least onepolymer with an elastomeric nature (D) or in a blend of (C1) and (D).

The polyolefin (C1) can be chosen from the polymers (A), (B) and thesyndiotactic polypropylene. (D) is a polymer with an elastomeric nature,that is to say that it can be an (i) elastomer within the meaning ofASTM D412, that is to say a material which can be drawn at ambienttemperature to two times its width, can be held thus for 5 minutes andthen, when it is released, it returns to its starting length, to withinless than about 10%, or (ii) a polymer which does not have exactly theseabove characteristics but which can be drawn and can returnsubstantially to its starting length.

The MFI of (D) is advantageously between 0.1 and 50.

Mention may be made, as example of polymers (D), of:

-   -   EPR (ethylene/propylene rubber) polymers and EPDM        (ethylene/propylene/diene) polymers;    -   polyethylenes obtained by metallocene catalysis and with a        density of less than 0.910 g/cm³;    -   polyethylenes of VLDPE type (very low density);    -   styrene elastomers, such as SBR (styrene/butadiene rubber)        elastomers, styrene/(styrene/butadiene/styrene (SBS) block        copolymers, styrene/ethylene/butene/styrene (SEBS) block        copolymers and styrene/isoprene/styrene (SIS) block copolymers;    -   copolymers of ethylene and of at least one ester of unsaturated        carboxylic acid (already defined in (A));    -   copolymers of ethylene and of at least one vinyl ester of        saturated carboxylic acid (already defined in (A)).

The amount of (C1) or (D) or (C1)+(D) is advantageously from 20 to 1 000and preferably 60 to 500 parts (by weight) per 10 parts of graftedsyndiotactic polypropylene. Advantageously, (C1) and (D) are used. Thepreferred proportions are such that (D)/(C1) is between 0 and 1 and moreparticularly between 0 and 0.5.

As regards the second form, the grafted isotactic polypropylene ismanufactured as mentioned above by grafting a blend comprising at least(B1) and optionally at least one polymer chosen from (A), (B2) and (B3).Advantageously, the proportion of (B1) is at least 50 and preferably 70%by weight of the blend to be grafted. This grafted isotactic propyleneis then diluted in syndiotactic propylene and optionally in at least onepolymer with an elastomeric nature (D). The polymer (D) has been definedabove.

The amount of syndiotactic polypropylene and optionally of (D) can befrom 20 to 1 000 and preferably 60 to 500 parts (by weight) per 10 partsof grafted isotactic polypropylene. Use is advantageously made ofsyndiotactic polypropylene and (D). The preferred proportions are suchthat the ratio of the amount of (D) to the syndiotactic polypropylene isbetween 0 and 1 and more particularly between 0 and 0.5.

The binder of the invention can be manufactured by the usual means forthermoplastics by melt blending the various constituents in Busstwin-screw extruders, mixers or roll mills.

The binder of the invention can also comprise various additives, such asantioxidants, ultraviolet absorbers, antistatic agents, pigments, dyes,nucleating agents, fillers, slip agents, lubricants, flame retardantsand antiblocking agents.

As regards the multilayer structure of the present invention, it iscomposed of the layer comprising the above binder and of a layer ofoxygen-comprising or nitrogen-comprising polar resin or of an inorganicoxide deposited on a polymer, such as PE, PET or EVOH or a metal layer.

Examples of polar resins which are preferred in the layer other than thebinder are polyamide resins, a saponified copolymer of ethylene and ofvinyl acetate, and polyesters.

More specifically, they comprise synthetic long-chain polyamides havingstructural units of the amide group in the main chain, such as PA-6,PA-6,6, PA-6,10, PA-11 and PA-12; a saponified copolymer of ethylene andof vinyl acetate having a degree of saponification of approximately 90mol % to 100 mol %, obtained by saponifying an ethylene/vinyl acetatecopolymer having an ethylene content from approximately 15 mol % toapproximately 60 mol %; polyesters, such as poly(ethyleneterephthalate), poly(butylene terephthalate) or poly(ethylenenaphthenate); and blends of these resins.

The layer of inorganic oxide can, for example, be silica, it isdeposited on a layer of PE, PET or EVOH. The structure of the inventiontherefore comprises, respectively: a binder layer, an SiO₂ (or SiO_(x))layer and either PE or PET or EVOH.

The metal layer can, for example, be a sheet, a film or a sheet of ametal, such as aluminium, iron, copper, tin and nickel, or an alloycontaining at least one of these metals as main constituent. Thethickness of the film or of the sheet can be suitably chosen and it is,for example, from approximately 0.01 to approximately 0.2 mm. It iscommon practice to degrease the surface of the metal layer beforelaminating the binder of the invention thereon. This layer can also be ametalloplastic layer, such as, for example, a sheet of aluminized PET.

It would not be departing from the scope of the invention if thepreceding structure were combined with other layers.

The invention also relates to the preceding structure combined on theside of the binder with a polyolefin-based layer (F). The polyolefin (F)can be chosen from the polymers (A) and (B) above.

These structures are of use in preparing packagings, for example rigidhollow bodies, such as bottles or jars, flexible bags or multilayerfilms.

The binders of the invention are of use for the following structures.

PE/binder/EVOH/binder/PE (PE denotes polyethylene)

PE/binder/EVOH

PE/binder/PA

PP/binder/PA

PP/binder/EVOH/binder/PP (PP denotes polypropylene).

These structures and these packagings can be manufactured bycoextrusion, lamination, extrusion-blow moulding and coating.

EXAMPLES

The following products were used:

sPP: Syndiotactic polypropylene. PP 3060 MN5: Isotactic copolymercomprising propylene/ethylene blocks with a density = 0.902 g/cm³ andwith an MFI = 6 (230° C./2.16 kg). PP 3050 MN1: Isotactic polypropylenehomopolymer with a density of 0.905 g/cm³ and an MFI of 5 (230° C./2.16kg). PP 3020 GN3: Random polypropylene copolymer with a density of 0.900g/cm³ and with an MVI (melt volume index) of 2 cm³/10 min (230° C./2.16kg). MAH: Maleic anhydride. PPC: Polypropylene grafted with maleicanhydride comprising 0.1% of MAH, with an MFI of 2 g/10 min (l90°C./2.16 kg). PPAM2: Polypropylene grafted with maleic anhydridecomprising 2.5% of MAH, with an MFI of 40 g/10 min (190° C./325 g).

The products are grafted with maleic anhydride. They are manufactured ina corotating twin-screw extruder of Leistritz type.

The extruder comprises 8 regions numbered Z1 to Z8, Z8 is situated atthe end of the extruder where the grafted products exit. The processingis carried out at the usual temperatures.

The maleic anhydride, on polyethylene powder, and the polypropylene tobe grafted are introduced into the region Z1 via two separate weightmetering devices.

The radical initiator, pure or diluted in an appropriate solvent, isintroduced via a metering pump into the region Z2. The temperatures inthe regions Z3, Z4 and Z5 are at least sufficient for 99.9% of theradical initiator to react before the region Z6. The initiator used is2,5-dimethyl-2,5-(di-tert-butyl)hexane (Luperox 10) (DHBP). The residuesfrom the radical initiator, the solvent and the unreacted maleicanhydride are degassed under vacuum in the region Z6.

The throughput for extrusion at the outlet of the region Z8 varies,according to the screw rate imposed, between 12 and 15 kg/h. The lace isgranulated after cooling.

The results of the grafting are collated in Table 1. The % valuesindicated for MAH and the initiator are with respect to thepolypropylene.

It is found that, for the isotactic polypropylene, the MFI changes from0.2 to 5.9 or 10.6 according to the proportion of DHBP added, i.e. anincrease by a factor of 30 or 50. By comparison, for the sameproportions of DHBP added, the MFI of the syndiotactic polypropylenechanges only from 0.7 to 6.6 or 14.3, i.e. an increase by a factor of 10or 20.

Cast technology was then used to produce a structure comprising 5layers:

PP/binder/EVOH/binder/PP, in which PP denotes the (isotactic)polypropylene, with respective thicknesses in μm: 20/10/10/10/50. Theresults are listed in Table 2 below. The peel strength between the PPand the binder on the thin side (PP 20 μm/binder 10 μm) was measured.The strength is expressed in N/15 mm at a drawing rate of 200 mm/min att0, that is to say immediately after the structure has been prepared.

TABLE 1 Powder Powder comprising formed from 7.5% of PE support MAH DHBPDHBP of the MAH Grafted MFI MFI MFI Poly- introduced introducedintroduced introduced MAH 190° C. 190° C. 190° C. propylene (%) (%) (%)(%) (%) 325 g 2.16 kg 5 kg PP3060 MN 5 1.5 0.1500 2.00 4 0.80 10.8 — —sPP — — — — — 0.0 0.7  2.3 sPP extr. # — — — — — 0.0 0.9  2.7 sPP 1.50.1500 2.00 4 0.54 1.8 14.3 42.5 sPP 1.5 0.1125 1.50 4 0.41 1.1 9.8 30.2sPP 1.5 0.0750 1.00 4 0.31 0.8 6.6 20.0 PP 3050 MN 1 — — — — — 0.2 not —measurable PP 3050 MN 1 1.5 0.1500 2.00 4 0.54 10.6 not — measurable PP3050 MN 1 1.5 0.0750 1.00 4 0.34 5.9 not — measurable #sPP havingalready been extruded

TABLE 2 Binder Peel strength at t0 s standard % by weight N/15 mmdeviation PPC 5.4 0.1 96% sPP 5.2 0.7  4% PPAM2 94% sPP 6.1 0.4  6%PPAM2 96% PP 3020GN3 5.8 0.6  4% PPAM2 94% PP 3020GN3 5.6 0.3   6% PPAM2

1. A composition comprising (I) syndiotactic polypropylene and (II) atleast one polymer being: (A), a polyethylene or a copolymer of ethylene,(B), any of (B1) isotactic polypropylene homopolymer or copolymer, (B2)poly(1-butene) homo- or copolymer or (B3) polystyrene homo- orcopolymer, or a blend of (A) and (B), said composition being graftedwith a functional monomer such that each of (I) and (II) is at leastpartially grafted with said functional monomer.
 2. A compositionaccording to claim 1, wherein the functional monomer is maleicanhydride.
 3. A coextrusion binder comprising the composition accordingto claim 1, diluted in at least one polyolefin (C1) or in at least oneelastomeric polymer (D) or in a blend of (C1) and (D).
 4. A coextrusionbinder according to claim 3, in which the amount of polyolefin (C1) orof elastomeric polymer (D) or of the blend of (C1) and (D) is from 20 to1000 and (by weight) per 10 parts of grafted syndiotactic polypropylene.5. A coextrusion binder according to claim 3, in which the amounts byweight of polyolefrn (C1) and of elastomeric polymer (D) are such thatthe weight ratio of (D)/(C1) is between 0 and
 1. 6. A multilayerstructure comprising: a layer comprising a coextrusion binder accordingto claim 3; and, directly attached to this layer, a layer (E) of apolyamide resin of a saponified copolymer of ethylene and of vinylacetate, of a polyester resin, or of an inorganic oxide deposited on apolyethylene, polyethylene terephthalate, EVOH, or on a metal ormetalloplastic layer.
 7. A structure according to claim 6, comprising apolyolefin-based layer (F) directly attached to the binder layer.
 8. Acomposition according to claim 3, wherein the functional monomer ismaleic anhydride.
 9. A coextrusion binder according to claim 4, in whichthe amounts by weight of polyolefin (C1) and of polymer with anelastomeric nature (D) are such that the weight ratio of (D)/(C1) isbetween 0 and
 1. 10. A composition according to claim 4, wherein thefunctional monomer is maleic anhydride.
 11. A composition according toclaim 5, wherein the functional monomer is maleic anhydride.
 12. Acomposition according to claim 9, wherein the functional monomer ismaleic anhydride.
 13. A composition according to claim 10, wherein thefunctional monomer is maleic anhydride.
 14. A coextrusion binderaccording to claim 10, wherein the blend contains from 60 to 500 partsby weight per 10 parts by weight of grafted isotactic polypropylene. 15.A coextrusion binder according to claim 11, wherein the ratio is between0 and 0.5% by weight.
 16. A multilayer structure comprising: a layercomprising a coextrusion binder according to claim 4; and, directlyattached to this layer, a layer (E) of a polyamide resin, of asaponified copolymer of ethylene and of vinyl acetate, of a polyesterresin, or of an inorganic oxide deposited on a polyethylene,polyethylene terephthalate, EVOH, or on a metal or metalloplastic layer.17. A multilayer structure comprising: a layer comprising a coextrusionbinder according to claim 5; and, directly attached to this layer, alayer (E) of a polyamide resin, of a saponified copolymer of ethyleneand of vinyl acetate, of a polyester resin, or of an inorganic oxidedeposited on a polyethylene, polyethylene terephthalate, EVOH, or on ametal or metalloplastic layer.